Its boundaries are the Río de La Plata to the East and South, the San Antonio River to the West and the Piraña Stream to the North.
Established in 1991, the Reserve is predominately an aquatic plant and marsh environment, characteristic of the Lower Paraná Delta. It hosts a wide range of flora and fauna, much of which has taken-up residence on the island over the years, and offers space for scientific research and environmental education.
The Reserve was given nature reserve designation in 2017, the same year in which it joined the Azara Foundation’s Private Reserve Programme. Achalay is also a member of the Argentine Network of Private Nature Reserves and has established an alliance with the Aves Argentinas Foundation, (the Argentine Bird Foundation).